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c8a6d91005
Commit 3ccfebedd8 ("powerpc, membarrier: Skip memory barrier in
switch_mm()") added some logic to skip the smp_mb() in
switch_mm_irqs_off() before the call to switch_mmu_context().
However, on non SMP smp_mb() is just a compiler barrier and doing
it unconditionaly is simpler than the logic used to check whether the
barrier is needed or not.
After the patch:
00000000 <switch_mm_irqs_off>:
...
c: 7c 04 18 40 cmplw r4,r3
10: 81 24 00 24 lwz r9,36(r4)
14: 91 25 04 c8 stw r9,1224(r5)
18: 4d 82 00 20 beqlr
1c: 48 00 00 00 b 1c <switch_mm_irqs_off+0x1c>
1c: R_PPC_REL24 switch_mmu_context
Before the patch:
00000000 <switch_mm_irqs_off>:
...
c: 7c 04 18 40 cmplw r4,r3
10: 81 24 00 24 lwz r9,36(r4)
14: 91 25 04 c8 stw r9,1224(r5)
18: 4d 82 00 20 beqlr
1c: 81 24 00 28 lwz r9,40(r4)
20: 71 29 00 0a andi. r9,r9,10
24: 40 82 00 34 bne 58 <switch_mm_irqs_off+0x58>
28: 48 00 00 00 b 28 <switch_mm_irqs_off+0x28>
28: R_PPC_REL24 switch_mmu_context
...
58: 2c 03 00 00 cmpwi r3,0
5c: 41 82 ff cc beq 28 <switch_mm_irqs_off+0x28>
60: 48 00 00 00 b 60 <switch_mm_irqs_off+0x60>
60: R_PPC_REL24 switch_mmu_context
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e9d501da0c59f60ca767b1b3ea4603fce6d02b9e.1625486440.git.christophe.leroy@csgroup.eu
28 lines
877 B
C
28 lines
877 B
C
#ifndef _ASM_POWERPC_MEMBARRIER_H
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#define _ASM_POWERPC_MEMBARRIER_H
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static inline void membarrier_arch_switch_mm(struct mm_struct *prev,
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struct mm_struct *next,
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struct task_struct *tsk)
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{
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/*
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* Only need the full barrier when switching between processes.
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* Barrier when switching from kernel to userspace is not
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* required here, given that it is implied by mmdrop(). Barrier
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* when switching from userspace to kernel is not needed after
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* store to rq->curr.
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*/
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if (IS_ENABLED(CONFIG_SMP) &&
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likely(!(atomic_read(&next->membarrier_state) &
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(MEMBARRIER_STATE_PRIVATE_EXPEDITED |
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MEMBARRIER_STATE_GLOBAL_EXPEDITED)) || !prev))
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return;
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/*
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* The membarrier system call requires a full memory barrier
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* after storing to rq->curr, before going back to user-space.
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*/
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smp_mb();
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}
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#endif /* _ASM_POWERPC_MEMBARRIER_H */
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